Machine for grinding twist drills



April 8, 1952 K. TRIPPEL 2,591,893

MACHINE FOR GRINDING TWIST DRILLS Filed May 24, 1947 2 swam-swam .1

INVENTOR. KARL TE/PPLL.

ATTORNE K April 8, 1952 K. TRIPPEL 2,591,893

' MACHINE FOR GRINDING TWIST DRILLS Filed May 24, 1947 2 SHEETS-SHEET 2 INVENTOR. KAR L TR/PPEL ATTORNEK 1 The problem Patented Apr. 8, 1952 h UNITED STATES PATENT OFFICE Y MACHINE FOR GRINDING TWIST DRILLS Karl Trippel, Choindez, Switzerland Application May 24, 1947, Serial No. 750,300

In Germany November 26, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires November 26, 1960 5 Claims. (o1. 51 219) ,This invention relates to machines for grinding twist drills.

Twist drills play an important part in finishing processes, and as these drills are still fregquently sharpened by hand grinding, which is .nota very accurate. or economical method,the

accuracy of the grinding suffers and the grinding ,process remains uneconomical. ,The commonest twist drills are these with a conical relief grinding. However, there are also drills the ridges or cutting faces of which are usually composed of two surfaces, the individual surfaces being concavely curved or fiat. Hitherof sockets could be provided without exchanging .csockets, especially on account of the rocking movement that has to be effected during the grinding. V v

underlying the invention is to be able to grind a large number of different sizes of drill on an apparatus that is as simple as possible. For this purpose, it is of fundamental importance to make aselection of a definite drill grinding which not only fulfills the requirements .of practice but even affords advantages for the solution of the problem with regard to the :set of tools required for the grinding. For thi purpose, the ridge faces of the drill are composed,

in the fundamentally known manner, of two surl 1aye, along the edge, a narrow hollow chamfer .and then, adjoining at the rear, a hollow ground part, has, for receiving the drills, a drum which is fixable with the aid of peripheral grooves and has a cylindrical-outer shell and a conical inner surface. For guiding the drills in succession, this drum contains bores which are obliquely arranged in the radial planes and are perpendicularto the conical inner surface. In addition, it

is provided on the outer shell with stops for the inserted drill. Thereceiving drum, which carries the particular drill, that is to be ground in an approximately horizontalplane and the axis of which lies at about the level of the axis of the grinding wheel, ismoved past the periphery of the grinding wheel in the straight-line direction of the shell. This machine has also an especially simple and advantageous receiving device for d ri lls in the case of which itispossible to effect r .2 i with the same means the grinding of a large number of drills of different sizes, the number of different sizes being considerably greater than has been possible to grind hitherto.

Further features of the invention are that the grinding bores for thicker drills are arranged near the hub of the drum and the guiding bores for the thinner drills are arranged near the free edge of the drum. The drill stops are in this case made plate-shaped. Finally, the axisof the drum that receives the drills can be swivelled horizontally in order to be able to obtain different point angles. v

An example of embodiment of the subjectmatter of the invention is represented in the accompanying drawings, of 'whichv Figure l is a front elevation of the machine; Figure 2 is aplan; i FigureB is a side elevation sectioned on the line 1-1 of Figure 2;

Figure 4 is a section of the receiving drum .with an example of five-hole rows; 1

Figure 5 shows a drill with ground surfaces? 1 Figure 5a. is an end view of a drill;

1 Figure dis a section through the adjusting device a drill and a drill grinding wheel can be rotated by means of a belt.

drive or directly by a motor. The use of a belt drive considerably reduces the cost of a. machine. It'is also possible to arrange grinding wheelson the two sides .of the drive, it then being possible for one wheel to serve for generalgrinding work or for pointing twist drills. A carriage 2 is moved in a dovetailed guide on the base plate I a spindle l and a nut 3 by means of a handwheel 5 near the grinding wheel. A guide plate 21 runs at right angles to the dovetailed guide in the carriage 2 and this guide plate 21 has, at the bottom, a rack in which a screw wheel 1. engages, so that the plate 21 can be moved by means ofa handle 9, to and froparallel to the section plane of the grinding wheel 24.; In this 3 way, a faultless grinding of the lips of a drill or of a narrow hollow chamfer is obtained, whilst the operating surface of the grinding wheel remains smooth and furrows or unevennesses are avoided. Since the rotating grinding wheel does not have to carry out any reciprocatory movement, the greatest accuracy of the grinding of the lips of a drill or of the narrow hollow chamfer is ensured. The shaft 8 of the screw wheel is rotatably mounted in the base plate I.

A pivot I3 is mounted on the guide plate 21. This pivot serves for receiving the swivel bearing III. on this guiding plate there is located in front a degree scale 6 which renders possible the adjustment of the desired point angle and the fixing of the selected position on the guiding plate 21 by tightening a lever nut I5. The funnel-shaped receiving drum I2 is mounted without play on an axle I I which is tight in the swivel bearing I0. This axle can be swivelled horizontally. Consequently, the cleaning of the machine is very simple, since the axle I I is only loosened in the swivel bearing I and the fixable 'drum- I2 is then taken off. The drum I2 has a cylindrical outer shell and a conical inner surface and, in addition, on its edge, peripheral grooves ,IB

riphery of the drum. The position of thedrill introduced, e. g., of the drill 23, in front of the grinding wheel is fixed in such a manner that The stops 32 serve the desired grinding results. also for this purpose both in the longitudinal direction and in the direction of rotation. If drills of different .pitch or spirals are used and if, on the other hand, the position of the drill lip to be ground is always to remain horizontal, it is important that the stop for the direction of 'rotation should be placed near the drill lip to be ground. This is rendered possible by uniting the twostops to form a plate-shaped stop 32 which is fixed on the drum in front of the point of the drill (Figures 4 and 9).

For the purpose of obtaining symmetrically ground drill lips or a narrow hollow chamfer, it is necessary to know the grinding depth to which the apparatus is set in order'to be able again to adjust, by resetting, the last drill lip at the end of the sharpening. For this purpose, a counting disc 33 arranged next to the handwheel 5, is emplayed in the known manner, which counting discis kept by a spring 34 with. a brake screw in the position of rest on the fixed hub located on the. carriage 2. On the outer shell of the counting disc 33 there is located a scale graduated in hundredths of a millimetre, on which scale the advanceof the spindle can be read off by means of a pointer 31. Fitted next to the handwheel is a knob 36 by means of which the counting disc 33 is rotated through the spindle 4. This is effected by the, conical, axle of the knob 33 pressing two clamping bolts 38 apart so that the latter press against the inner wall of the counting disc 33 and drive the counting wheel when the handwheel 5 is rotated. Immediately after the pressure on the knob is released, the spring 35 releases the two clamping bolts and again releases the counting disc 33. The reading range on the counting disc amounts to about mm. for the group of small drills. The corresponding stroke of the counting disc is limited by a pin 39 which is mounted on the base plate I and which projects into a recess in the counting disc 33. In this way, the adjustment to too great a grinding depth and, consequently, the burning of the drill, are avoided. If the grinding depth is to be adjusted, the hand resting on the handwheel 5, by pressing on the knob 36, couples the counting disc 33 with the spindle I and then rotates the spindle 4 through about, for example, 4 graduation marks, i. e., /100 mm. The counting disc 33, which is thereupon again released, now remains at rest on the graduation mark concerned until the grinding is finished. Onesidedness of the ground part is then removed by pressing on the knob 36 and rotating the counting disc 33 to the zero position.

The reason for the oblique position of the grinding wheel is that, with a belt drive, by pressing off the grinding motor or the grinding support, complete freedom of movement results for the handwheel 5, the operative lever 9 and the pointing disc 40. Owing to the oblique position of the grinding wheel, the radius of grinding on the work piece is now greater and the ground surface and relief-ground surface are correspondingly flatter. The diameter of the grinding wheel and the width and, consequently, the thickness of the motor can, for this reason, be made somewhat smaller. The turning of the grinding wheel is effected by sticking the diamond holder, in the normal position of 116 to 120, into a bore in the drum I2 and moving it to and fro in front of the grinding wheel by means of the lever 9.

The surface of the base plate I has troughshaped depressions which are intended for receiving the twist drills to be ground.

The sharpening of a twist drill is carried out in the following manner:

The locking pin I1 is disengaged, the drum I2 is adjusted to the desired diameter of drill and the locking pin is engaged. The drill is now inserted up to the stop 32 and the lever 9 and the handwheel 5 are operated until sparks are produced by the drill and the grinding wheel. The setting of the grinding depth then takes place by pressing the knob 36 on to the handwheel 5 and rotating the handwheel to the desired graduation mark. The knob 36 is then released. Thereupon, the first drill lip is ground'by moving the lever 9, the drill is then withdrawn and a rotation through is effected. Thereupon,

the drill is again pushed forward up to the stop and further grinding is carried out until the two lips are sharp.

The locking pin I1 is now pushed out, the drum is rotated one groove downwards and the locking pin is then again pressed in. Thereupon, the application of the drill to the grinding Wheel is effected by means of the handwheel 5 and the setting of the grinding depth, with the result that a hollow chamfer is produced. The onesidedness of the drill lips is removed bypressing the knob 36 to the handwheel and by, at the same time, rotating the spindle back to the zero position. The drill is then rotated through 180 until the last lip is ground. The grinding of the two lips is then at the same amount. The grinding of the chamfer may be dispensed with in the case of smaller drills.

If another point angle is ground on the drill instead of the ordinary point angle, the lever nuts l5 are loosened, the guiding drum I2 is adjusted to the desired number of degrees and the lever nuts l5 are then again tightened whereupon the grinding of the drill lips can take place.

Machines for sharpening left-hand drills have a guiding drum with correspondingly oppositely directed guiding holes (Figure as indicated by the angle 3 I. 7

On the other end of the shaft of the motor or, in the case of a belt drive, on the shaft of the grinding wheel, there is provided a second grinding wheel 40 which, after the sharpening may be employed for the pointing.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. A machine for grinding twist drills having cutting faces formed with a narrow hollow chamfer along their edges, and with a hollow ground part adjoining such edges at the rear; said machine comprising a base, a grinding wheel rotatably supported'on said base with the axis thereof disposed in a horizontal plane, a support slidable on said base in a path of travel related angularly to the axis of said wheel, a drum having a cylindrical outer surface and a conical inner surface rotatably mounted on said support with the axis of rotation of said drum disposed in said horizontal plane of the grinding wheel axis, angularly spaced grooves formed in the outer surface of said drum, a locking pin carried by said support and engaging in a selected one of said grooves for retaining said drum in a selected one of a plurality of angularly adjusted positions, a plurality of sets of bores formed in said drum in angularly spaced radial planes of said drum, each of said bores being perpendicular to said conical inner surface of said drum and adapted to'receive a drill to be ground, and stops carried by the outer surface of said drum adjacent the outer end of each bore for retaining a drill in the associated bore whereby said drum is adapted to support a drill for grinding in a substantially horizontal plane at the level of the axis of the grinding wheel for movement past the periphery of the wheel in a direction parallel to the. path of travel of said support.

2. A machine according to claim 1, wherein said drum is rotatably supported at one end, and wherein the bores of each of said sets are of successively increasing diameter toward said one end of the drum whereby said bores are adapted to receive drills of varied diameters.

3. A machine according to claim 1, wherein each of said stops includes a plate pivoted at one end on the outer surface of said drum and formed with a notch in the swinging end thereof within which a turn of a drill in the associated bore may engage. a

4. A machine according to claim 1, wherein said support includes a plate slidable on said base and a standard pivoted on said plate for swinging about a vertical axis whereby said drum is adapted to be swivelled in a horizontal plane. 5. A machine for grinding twist drills comprising a base, a dovetail guide formed in said base, a carriage slidable on said guide, a guide formed in said carriage at right angles to the direction of movement of said carriage relative to said base, a plate slidably mounted upon said guide formed on said carriage, a vertical pivot on said plate, a standard rotatable on said pivot for swinging about a vertical axis, a grinding wheel, means rotatably mounting said wheel on said base with the axis of rotation of said wheel disposed in a horizontal plane, a drum having a cylindrical outer surface and a hub on one end thereof, means extending through said hub rotatably mounting said drum on said standard with the axis of rotation of said drum lying in the horizontal plane passing through the axis of rotation of said wheel, means maintaining said drum in a selected rotated position, said drum being formed with a conical inner surface open-.

ing at the other end thereof, a plurality of sets of bores formed in said drum in angularly spaced radial planes, each of said bores being perpendicular to said inner surface of said drum and adapted to receive a drill to be ground, and stop means carried by said drum at the outer surface thereof adjacent each of said bores for engagement with a drill in the associated bore to hold the drill in position to be ground whereby said drum is adapted to support a drill for grinding in a substantially horizontal plane at the level of the axis of rotation of the grinding wheel for movement in-right angularly related directions.

KARL TRIPPEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number N ame Date 1,231,258 Horvath June 26, 1917 1,737,415 Gibney Nov. 26, 1929 FOREIGN PATENTS Number Country Date 230,117 Switzerland Mar. 1, 1944 

